As commonly known, clamping mechanisms of the over-center type are used in many applications where it is important that a loss of air or oil pressure in the cylinder operating the clamping mechanism will not result in release of the mechanism. This requires spring loaded clamps as one method of solution for effective travel past a dead center position with sufficient residual load generated by the springs in the clamp to hold the work. The normal spring box assembly consists of a sandwich construction of a clamp block backed by die springs located inside a spring box attached to the pivot linkages of the clamping mechanism. Stripper bolts are used through the springs to hold the spring box assembly together.
In certain applications, such as in clamping mechanisms for supporting the anodes of an electrolytic cell for the production of aluminum as disclosed in U.S. Pat. No. 3,484,856 issued Dec. 16, 1969, the anode rods have inherent positional variations; they are bent after several cycles of operation, and they may be slightly angled during installation. Therefore, the clamp blocks often hang up on the anode rod sides during installation. This generates high direct shear and eccentric shear loads which must be resisted by the stripper bolts. Therefore, a high incidence of stripper bolt breakage has resulted when using the above spring box assembly in the clamping mechanisms of the over-center type.